1. Field of the Invention
The present invention relates to a semiconductor laser having a ridge-shaped current concentration portion, and more particularly to a semiconductor laser obtained by improving a shape, and a manufacturing method thereof.
2. Description of the Related Art
In recent years, there has been developed a semiconductor laser having a ridge-shaped current concentration portion (ridge portion) in a double hetero structure as a light source having a short wavelength and a high output. In this type of laser, in order to obtain a target laser characteristic, strict control over a ridge width is important. In particular, in a semiconductor laser which is used as a high-output light source for a CD-R or a DVD-R, a reduction in a ridge width is required, as well as strict control of the ridge width.
However, in a generally used wet etching process, a ridge side surface after etching processing has a sequential taper shape. Therefore, when the ridge width is reduced, there occur problems of an increase in an operating voltage caused due to a reduction in an upper ridge width and occurrence of a kink in the optical output—current characteristic.
It is to be noted that both the width and the height of the ridge portion must be strictly controlled. In a prior art, an etching stop layer is inserted in the middle of a clad layer, and etching of the clad layer is stopped by the etching stop layer, thereby controlling the height of the ridge portion. This etching is possible by wet etching, but dry etching such as reactive ion etching (RIE) can hardly assuredly stop etching by using the etching stop layer. Therefore, wet etching must be used for etching in order to form the ridge, and the ridge shape cannot be prevented from having the sequential tapered shape in actual practice.
As described above, conventionally, in the semiconductor laser having the ridge portion, it is hard to form the side surface of the ridge portion to be vertical, which is a factor preventing realization of a high output laser. Therefore, there has been demanded realization of a high-output semiconductor laser that can realize a ridge portion whose side surfaces are vertical, and prevent a kink in the optical output—current characteristic from occurring, and a manufacturing method of the semiconductor laser.